136 lines
4.0 KiB
C
136 lines
4.0 KiB
C
#include <unistd.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <errno.h>
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#include <string.h>
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#include <stdlib.h>
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#include <stdio.h>
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#define RBUFSZ 4096
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#define WBUFSZ 4096
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static void die_perror(const char *what, const char *path, int exit_code) {
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int saved = errno;
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char msg[512];
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if (path) {
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snprintf(msg, sizeof(msg), "%s: %s: %s\n", what, path, strerror(saved));
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} else {
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snprintf(msg, sizeof(msg), "%s: %s\n", what, strerror(saved));
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}
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(void) write(STDERR_FILENO, msg, strlen(msg));
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_exit(exit_code);
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}
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static long long parse_ll(const char *s) {
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char *end = NULL;
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errno = 0;
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long long v = strtoll(s, &end, 10);
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if (errno != 0 || end == s || *end != '\0' || v < 0) {
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errno = EINVAL;
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return -1;
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}
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return v;
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}
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int main(int argc, char *argv[]) {
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if (argc != 4) {
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const char *usage =
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"Usage: lab1_var12 <input.txt> <output.txt> <max_replacements>\n"
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"Variant 12: per line, take the first character as key and replace its matches with spaces,\n"
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" stopping after <max_replacements> replacements globally.\n";
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(void) write(STDERR_FILENO, usage, strlen(usage));
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return -1;
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}
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const char *in_path = argv[1];
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const char *out_path = argv[2];
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long long cap = parse_ll(argv[3]);
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if (cap < 0) {
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die_perror("invalid max_replacements", argv[3], -1);
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}
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int in_fd = open(in_path, O_RDONLY);
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if (in_fd < 0) {
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die_perror("open input failed", in_path, -1);
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}
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mode_t filePerms = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH; /* rw-rw-rw- */
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int out_fd = open(out_path, O_CREAT | O_WRONLY | O_TRUNC, filePerms);
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if (out_fd < 0) {
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die_perror("open output failed", out_path, -1);
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}
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char rbuf[RBUFSZ];
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char wbuf[WBUFSZ];
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size_t wlen = 0;
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long long total_replacements = 0;
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int at_line_start = 1;
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unsigned char line_key = 0;
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int replacing_enabled = 1; /* flips to 0 when cap reached */
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for (;;) {
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ssize_t n = read(in_fd, rbuf, sizeof(rbuf));
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if (n > 0) {
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for (ssize_t i = 0; i < n; i++) {
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unsigned char c = (unsigned char) rbuf[i];
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if (at_line_start) {
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line_key = c;
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at_line_start = 0;
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}
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unsigned char outc = c;
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if (c == '\n') {
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at_line_start = 1;
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} else if (replacing_enabled && c == line_key) {
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if (total_replacements < cap) {
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outc = ' ';
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total_replacements++;
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if (total_replacements == cap) {
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replacing_enabled = 0; /* hit the cap; from now on just copy */
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}
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} else {
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replacing_enabled = 0;
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}
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}
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if (wlen == sizeof(wbuf)) {
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ssize_t wrote = write(out_fd, wbuf, wlen);
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if (wrote < 0 || (size_t) wrote != wlen) {
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die_perror("write failed", out_path, -1);
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}
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wlen = 0;
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}
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wbuf[wlen++] = (char) outc;
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}
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} else if (n == 0) {
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if (wlen > 0) {
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ssize_t wrote = write(out_fd, wbuf, wlen);
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if (wrote < 0 || (size_t) wrote != wlen) {
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die_perror("write failed", out_path, -1);
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}
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wlen = 0;
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}
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break;
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} else {
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die_perror("read failed", in_path, -1);
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}
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}
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if (close(in_fd) < 0) {
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die_perror("close input failed", in_path, -1);
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}
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if (close(out_fd) < 0) {
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die_perror("close output failed", out_path, -1);
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}
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char res[64];
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int m = snprintf(res, sizeof(res), "%lld\n", total_replacements);
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if (m > 0) {
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(void) write(STDOUT_FILENO, res, (size_t) m);
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}
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return 0;
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}
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